A similar situation with the M3 LTW. Few takers, even for a limited edition, when they were new, so they sat in showrooms. Perhaps not unexpected, for only a slightly more hardcore version (Al doors from the Euro model, strut brace, rear wing, forged wheels, unique seat trim, M flag stickers good for +50hp; just kidding) that had other features stripped away (no radio, no A/C), for a higher price. A parts bin concoction, aimed at a limited audience, really.
The E36/8 didn't suffer from that, but its quirky looks meant that it would by appreciated by few.
In that era, the BMW 5-speeds in the smaller cars had similar, if not identical ratios, with a direct drive fifth gear. They played with the final drive ratio to do the heavy lifting. The 6-speeds brought an overdrive top gear, but IIRC, didn't change much else.
"Collectable" is a loaded term, that has no meaning until proven by someone willing to pay the price, but the fact was that they weren't desired models at the time. That may have changed, especially for the '01 models with the S54, but it's still a limited audience, even if more have discovered and recognized its charms.
An E30 M3, made in much higher numbers, will still have more value, and desirability, and people willing to pay their current prices.